Our expert says:
A couple of main reasons, and a number of smaller, quite complex reasons. I’m not sure how broad your understanding of human biology is, and so hopefully this is not too technical.
The first reason is that your heart muscle gets stronger. This means that each time the heart beats, it pumps more blood to the body. Now, if the heart is required to pump a certain volume each minute, and it is able to pump more because it is stronger, then it stands to reason that it needs to pump less. So, that is one reason.
The second is that the nervous system control of the heart is altered. You see, the heart is a unique muscle in that it generates its own electrical activity, but it still is under the control of the higher central nervous system. Now, there are two divisions of what is called the autonomic nervous system (the part of the nervous system that controls the automatic functions like heart rate, breathing, digestion etc). These two divisions are the sympathetic and parasympathetic systems. When the sympathetic system is stimulated, then heart rate goes up. You often hear the sympathetic system referred to as the ‘fight or flight’ system. If the parasympathetic system is active, the heart rate slows down. Exactly how this happens is very complex, and I’ll go into detail if you ask me to, but it’s not really that necessary. So, with physical training, the parasympathetic division of the autonomic nervous system becomes more and more dominant – it’s almost as though the training and exercise is not perceived as a stress like it was before. As a result, the heart rate will go down during exercise and at rest.
I hope this was not too complicated and helps explain what you observe.
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